This invention relates generally to luminescent display devices and to a method of manufacturing the same. More particularly the invention relates to gas plasma display devices.
It is well known to produce light by the passage of electricity through gases. This phenomenon has been used in lighted signs which display numerals, characters, symbols, graphics and the like, such as in neon signs for example. Gases commonly used for this purpose are neon, argon, mercury vapor, or mixtures thereof.
U.S. Pat. No. 5,383,295 shows a rather common type of flat display device wherein three glass or plastic plates are fused together to form a sandwich, the outer plates being continuous planes and the central plate having a major portion of its central part removed forming a chamber for containing the desired inert gas. A quantity of frit or beads fills the interior chamber and serves as a separator providing uniform space between the plates and a multitude of discharge channels for the electrical discharge produced by a power supply of radio frequency voltage fed by an electrode to the interior chamber. The glass beads serve to resist collapse of the outer surface plates, particularly during fabrication of the device, and when in use maintain uniform spacing between central areas of the outer plates. A tubular element attached centrally to one of the outer plates at a hole therethrough is used to evacuate the interior chamber and introduce an inert gas into the chamber. An electrode is then mounted in the tubular element in contacting relationship with the gas so that voltage supplied through the electrode ionizes the gas to produce fingers of light discharge extending radially outwardly from the center in the intersticial spaces between the beads thereby resulting in the desired display. The teachings of this patent are incorporated by reference herein.
U.S. Pat. No. 5,126,632 shows a display device similar to that discussed above wherein an electrode surface is provided on at least one side of the gas space for ionizing the gas and may be indicia shaped, or other graphic image shaped, to produce a shaped pattern of light for use as a sign, indicator or similar device. therethrough
U.S. Pat. No. 5,281,898 shows a glass double walled enclosure of cylindrical or spherical shape defining a chamber for containing an ionized gas discharge among dielectric pellets or beads. Electrodes are attached to ends of the enclosure and are connected to a transformer for supplying high voltage sufficient to produce visible discharges in the gas discharge area.
U.S. Pat. No. 4,403,831 shows a display device wherein two panels are sealed at their edges in spaced relation to provide a discharge chamber therebetween. Electrodes are positioned on opposing spaced surfaces of the panels in the chamber and spaced glass beads are positioned between panels in the chamber to act as spacers.
These prior art devices have the disadvantages of requiring numerous separate parts adding to the cost of materials and fabrication of the devices as well as excessive amounts of gas. In addition, shapes and configurations of images to be produced by the light discharge are unduly limited.
It is a principle object of the invention to provide a luminous display device which overcomes the above disadvantages by having a minimum number of parts and minimum gas requirement which minimizes the cost of materials, simplifies the assembly procedure, and reduces fabrication costs.
It is a further object of the invention to provide a luminous display device having a central pattern area that can be made in a large variation of shapes.
It is another object of the invention to provide a method of producing a luminous display device which is simplified relative to previous methods required for such devices having a greater number of parts.
The above objects are achieved by the invention wherein the display device is made of only two parts, the first of which is planar in shape and the second of which has an integral gas containing cavity or recess formed therein together with a plurality of semi-spherical or other shaped elements also integral with the second part and positioned in the cavity. The display device can also be curved in shape, or otherwise shaped such as undulated for example, whereby the first and second parts, the cavity and array of semi-spherical elements therein all have the same or corresponding shape. More particularly, the two parts are made of glass or plastic material and at least the first part is transparent. The second part is preferably molded to form the cavity therein and the array of semi-spherical elements protruding from the base of the cavity. The first and second parts are fused together at their peripheral areas to form a sealed gas discharge chamber therebetween with the semi-spherical elements protruding from the base of the cavity toward the first part and in closely spaced proximity thereto so that the interstices between the semi-spherical protrusions provide channels or paths for guiding the light discharges in the form of fingers or streaks through the device to produce the desired display. A hole is provided in the first or second part having an inner end communicating with the chamber and an outer end communicating with a tubular element mounted on the first or second part used for evacuating and filling the chamber with the desired inert gas. An electrode is mounted and supported in the tubular element and is connectable to a power source for ionizing the gas thereby producing the light discharges through the gas in the chamber. The hole is positioned off center with respect to the generally geometric center of the chamber or array of semispherical protrusions, for example about half the distance between the center and the periphery of the chamber.
The device of this invention is made by the method wherein the first part is cut from a sheet of glass, or molded, the second part is molded in a suitable mold producing a cavity having a base in one side of a glass member and a plurality of protuberances protruding from the base toward the open side of the cavity, the protuberances having the shape of semi-spherical elements, or other suitable shapes, closely spaced with respect to each other to provide channels or interstices therebetween, placing the first part over the cavity and in contacting relationship with the peripheral area of the second part around the cavity, and fusing the contacting areas together to seal the cavity and form a light discharge chamber in the joined assembly. A hole is made through the first or second part communicating at its inner end with the chamber at a position off center with respect to the area covered by the chamber, preferably about half the distance between the geometric center and periphery of the chamber. A tubular member is connected at one end to the outer end of the hole for use in evacuating and filling the chamber with the desired inert gas and also for housing the electrode which is mounted therein. The hole can be made during the molding of the first or second part or by drilling after the respective part has been made.